Laser light receivers (also referred to herein as “laser receivers,” “laser light detectors,” or “light beam receivers”) have been available in the past for use in precisely determining the proper elevation on construction job sites. The standard method for using such detectors is to mount a rotating laser light source at a particular elevation on a construction job site, then mount the laser light detector on a piece of equipment (such as on the blade of a bulldozer) to let the operator of the equipment know precisely the elevation of the equipment while it is in use. For example, the laser light detector could be mounted on a pole attached to the blade of a bulldozer, so the operator of the bulldozer could keep the blade at the correct position while grading the land to the precise elevation desired.
To be most effective, a laser light detector would have an easily viewable display that gives the elevation indication to a person who is sited a few feet from the detector. In addition, a laser light detector used on a machine would normally have some to type of photosensor (such as a photodiode or other type of photo-sensitive device) on all four corners of the detector's enclosure/housing, so that it could detect laser light coming from any direction. Typical laser light detectors must operate within a one hundred millisecond cycle time, since most rotating laser light sources rotate at 600 rpm.
Many laser sources used as rotating laser light sources operate in either the infrared or red light frequency spectrum. For example, infrared laser diodes operating at 780 nm wavelength are commonly used, as well as red light helium-neon gas lasers, operating at 633 nm wavelength. Moreover, red light laser diodes are now popular in many varieties, which operate at several different wavelengths from 635 nm through 670 nm. In addition, some rotating laser light sources are now available that operate in green light frequency spectrum, such as at a wavelength of 532 nm. The laser light is typically collimated. Various rotating laser light sources are available having beam sizes from as small as one-quarter inch in diameter to at least as large as three-quarter inches in diameter.
Laser light detectors are typically available in two types of models: a “machine control receiver” and a “hand-held receiver”. The machine control receiver is typically mounted on a piece of equipment, such as a bulldozer, and used in the manner discussed above. The hand-held receiver is typically a smaller device which can be carried by a typical construction worker to be used to detect the elevation of locations at a moment's notice. It should be noted that a machine control receiver may be used to directly control certain movements of the machine, and thus, that receiver might not include a display.
Currently, there are laser light receivers available on the market that are able to detect light only in the red and infrared (IR) spectra, while other available laser light receivers are able to detect light only in the green spectrum. However, there are no laser light receivers that are capable of detecting all three of these ranges of laser light. This is largely due to the fact that these receivers generally have an optical filter in front of the light sensor that transmits only the narrowest range of wavelengths necessary to allow the desired wavelength of laser light to pass through, while blocking as much of the remaining spectrum of light as possible. This is done to reduce the susceptibility of the unit to unwanted “stray” light, such as light from fluorescent lights, or, to a lesser degree, sunlight. The unwanted light, produced by “interference sources,” can sometimes be difficult for the receiver to distinguish from the desired laser light, thus causing erratic and/or errant information to be to conveyed from the receiver to the user. Such unwanted light is also referred to herein as an “unwanted interference light signal,” or light caused by interference light sources, such as fluorescent lights or strobe lights.
Typical laser receivers used on construction jobsites that are sensitive to only red and IR spectra may have little trouble in rejecting many fluorescent light sources, because most of the fluorescent light output occurs at wavelengths other than the red or infrared spectra. Therefore the optical filters that can be used on such red/IR laser receivers can, by themselves, reject most of the fluorescent light energy before reaching the photosensors mounted on the laser receiver units. It must be recognized, however, that strong fluorescent lights, and also strobe lights, are still able to cause some problems, even for laser receivers that are sensitive only to red/IR light.
However, laser receivers that are sensitive to green laser light must, by their nature, be sensitive to wavelengths that likely will include some of the energy produced by fluorescent light sources. Such laser receivers must either be permanently de-sensitized to the interfering fluorescent “stray” light energy, or must have a sensitivity circuit that can be adjusted to de-sensitize to such interfering fluorescent “stray” light energy. Otherwise, the laser receiver might constantly give false readings every time it is used in an (indoor) environment that includes fluorescent light sources. Since many laser receivers produce an audible “chirp” when detecting electromagnetic (light) energy at their photosensors, due to having some type of piezoelectric “speaker” mounted on board, those types of laser receivers will either constantly, or intermittently, emit a distinctive “chirping” noise when exposed to the interfering fluorescent light sources. When this occurs, the user typically becomes quickly aware that the laser receiver's indications cannot always be trusted, because the on-grade, above-grade, or below-grade readings will not likely be accurate in those operating conditions.
Another method that is sometimes employed to allow a receiver to more readily distinguish the laser light from other light sources is to modulate the transmitted laser light at a specific frequency, and design the receiver so that it “looks” only for light that is modulated at that specific modulation frequency. The disadvantage of this approach is that the receiver becomes more expensive to produce due to the more complex nature of the electronics required to allow the receiver to discern this discrete frequency. Additionally, the laser transmitter becomes a bit more expensive as well, in order to produce this modulated to beam. Furthermore, each modulated light receiver would need to be “matched” to a particular model of laser transmitter, and hence such a receiver would not be “universal” in the least.
There are no known laser receiver products that are capable of detecting green laser light, red laser light, and infrared light, all within a single unitary package. This is mainly true because the design considerations for green laser light receivers are quite different than the design considerations for red or infrared laser light receivers. Thus the two different visible light wavelengths that are used in existing transmitters (i.e., green light and red light) have created a chasm that has not been bridged by known laser receivers.
As noted above, currently there are laser receivers on the market that can detect light in the red and infrared (IR) spectra, and other laser receivers that can detect light in the green spectrum only, but not one that works for all three of these ranges of laser light. It would be desirable to have a single laser receiver unit that can effectively detect laser light in all three of these wavelength ranges, as some customers might already have (or need to have in the future) a variety of laser transmitters on-hand that operate at more than one, or all, of these wavelengths. This would not only increase flexibility for the customer, but it would also reduce inventory of the manufacturer and dealer, who otherwise would need to produce and stock different receivers to work with the different wavelengths of laser light.